Problem: In her language class, Nadia took 4 tests. Her scores were 87, 91, 81, and 85. What was her average score on the tests?
Explanation: The average is the sum of her scores divided by the number of scores. There are 4 scores and their sum is $87 + 91 + 81 + 85 = 344$ Her average score is $344 \div 4 = 86$.